Zinc ion has been used in oral products for some time now. In dentrifices, it has been employed as a tartar control agent. In mouthwashes, it is used as a bacteriocide (U.S. Pat. No. 5,455,023) and to combat malodor.
Bicarbonate has been used in oral products for a variety of purposes including, but not limited to, buffering capacity, alkalinizing agent, as an abrasive (as solid sodium bicarbonate particles),for deodorizing activity, and because it provides for a clean "mouthfeel" and a refreshing aftertaste in the oral cavity. Exemplary patents dealing with mouthwashes or rinses having bicarbonate included include, but are not limited to U.S. Pat. No. 4,132,770; U.S. Pat. No. 4,312,889; U.S. Pat. No. 4,666,708; U.S. Pat. No. 5,185,153; U.S. Pat. No.5,302,373; U.S. Pat. No. 5,330,749, U.S. Pat. No. 5,455,023; U.S. Pat. No. 5,541,165; and U.S. Pat. No. 5,587,147; all of which are incorporated herein by reference.
It has therefore been deemed advantageous to try to combine, in a single formulation, both zinc containing compounds and bicarbonate containing compounds. Unfortunately this has not been possible. Zinc ion reacts with bicarbonate ion to result in liberation of carbon dioxide and the formation of various insoluble basic salts of zinc and carbonate. Attempts to get around this technical difficulty have included keeping the two components separated in different compartment or containers until ready for use; encapsulating one or both of the ingredients; or presenting one or both of the components in slightly soluble form so that the two species are in limited contact until diluted by the user in the course of using the product, among others.
Examples of encapsulating one or both components include U.S. Pat. No. 5,302,373; U.S. Pat. No. 5,330,749; and U.S. Pat. No. 5,455,023. Examples of dual compartment dispensing include U.S. Pat. No. 5,456,902; U.S. Pat. No. 5,554,358; U.S. Pat. No. 5,616,313; and U.S. Pat. No. 5,632,972. Examples of complexation include U.S. Pat. No. 5,587,147. Typical of the presentation of one or more of the components in an insoluble or slightly soluble form until use is in the toothpaste, tooth gel and tooth powder area where remaining in solution during storage is not a critical requirement to meet.
However, mouthwashes cannot present with precipitates during storage and still be considered suitable delivery vehicles for the components they contain. Additionally, dual dispensing systems are inconvenient for the user and generally not desirable. As such, there has been a long felt need for a single phase stable mouthwash solution having both zinc ion containing compounds and bicarbonate ion containing compounds, each in solution.